Mozilla has announced plans to integrate its Firefox web browser with Metro for Windows 8 - including Gecko. "Windows 8 contains two application environments, 'Classic' and 'Metro'. Classic is very similar to the Windows 7 environment at this time, it requires a simple evolution of the current Firefox Windows product. Metro is an entirely new environment and requires a new Firefox front end and system integration points. The feature goal here is a new Gecko based browser built for and integrated with the Metro environment. Firefox on Metro, like all other Metro apps will be full screen, focused on touch interactions, and connected to the rest of the Metro environment through Windows 8 contracts." I haven't checked - does Microsoft allow different rendering engines?